Blood pressure monitoring is an important indicator of a wearer's cardiovascular status. Many devices allow blood pressure to be measured by manual or digital sphygmomanometer systems that utilize an inflatable cuff applied to a person's arm. These devices often include an inflatable cuff to restrict blood flow and a device capable of measuring the pressure.
In a typical blood pressure monitoring system, a hand actuated pump or an electric motor inflates the inflatable cuff to a pressure level at or above the expected systolic pressure of the wearer and high enough to occlude an artery. Automated or motorized blood pressure monitoring systems use a motor or pump to inflate the inflatable cuff, while manual blood pressure monitors typically use an inflation bulb. As the air from the inflatable cuff is slowly released, the wearer's blood pressure can be determined by detecting Korotkoff sounds using a stethoscope or other detection device placed over an artery.
However, both systems have their drawbacks. For example, these systems can cause pain or discomfort to the wearer. Other adverse effect can include limb edema, venous stasis, peripheral neuropathy, etc., or simply wearer interruption. In addition, manual systems make it difficult to measure blood pressure during inflation of the inflatable cuff due to the difficult of inflating the inflatable cuff at an approximately constant rate using an inflation bulb. Furthermore, motorized blood pressure monitors are often noisy and can disturb wearers at rest. In addition to auditory noise in automated or motorized systems, the motors can cause electrical noise in sensor signals making signal processing used to identify reference points for blood pressure detection unreliable and difficult.
Gas canisters, which are frequently used to supply gas in a fast and efficient manner, can be used in place of the motor and pump. However, due to the relatively high pressure of the gas inside the gas canister, care must be used when puncturing the seal of the gas canister to allow the gas to exit. To alleviate this danger, the nozzle of many gas canisters are threaded to engage with a complementary threaded release valve. A user inserts the nozzle of the gas canister into the release valve and then rotates the gas canister to engage the threads. Once the gas canister is sufficiently screwed into the release valve, a sharp point of the release valve punctures the top of the canister and allows the gas to exit.
However, there are several drawbacks to this approach. For example, the threads of the gas canister or the release valve may be stripped or may not align properly. In addition, the gas canister is left exposed, and a user may unwittingly unscrew a partially filled gas canister from the release valve. Furthermore, once punctured, many release valves do not provide any mechanism for controlling, or stopping, the flow of gas.